The goal of this project is to study the host response to onchorecal infection in order to understand the pathogenesis of clinical disease, the immune mechanisms operative in the persistence of the parasite within the host and in protective immunity, and to develop improved immunodiagnostic techniques. The initial phase of this project has involved a detailed clinical and laboratory assessment of the severe side effects (Mazzotti reaction) that accompany treatment of the infection and limit the potential of mass chemotherapy for onchocerciasis. Twenty-five patients were treated at a research center in Ghana and subjected to intensive immunologic and clinical evaluation as their prolonged Mazzotti reactions developed over the first week of therapy. The results from the study are currently being accumulated. Evaluation of IgE and IgG antibodies from patients with onchocerciasis has suggested that there is greater species specificity (i.e. less cross-reactivity), and therefore more potential for practical immunodiagnosis, in the IgE antibody system. The antigens and allergens underlying these specific responses are now being identified and isolated.